A standard flat key, as opposed to an axially bitted tubular key, has an elongated blade formed along one or both edges with bitting that coacts with tumblers carried in the plug of the lock for the key. In a standard system with seven bits each of which can be at four or five different levels, the number of combinations available is large but by no means impossible to discover by random action. In addition such a lock frequently can be forced relatively easily as the physical strength of a small number of slim tumblers, which are all that block rotation of the plug in the cylinder, is small.
Furthermore picking such a lock when the plug is slightly loose in the housing is a simple matter of sliding a blade pick between the plug and housing while sequentially working the tumblers in and out to force the blade through the split between the tumblers.
A second line of security provided by a standard key is in the form of warding, that is grooves and ridges that extend along the faces of the blade of the key to impart to same a characteristic cross section. Such warding makes it impossible to fit into the lock a key or other tool that is not of the right section, and it has even been suggested to employ these grooves and ridges with further devices such as elements that prevent retraction of the key unless it is in a particular position. Such formations nonetheless add little to the number of combinations a key can be set to and do little to increase the physical resistance of the lock.